Recently efficient maintenance-free rechargeable sealed lead/acid storage batteries utilizing a "starved electrolyte" concept have been introduced commercially. Various aspects of batteries of this type are disclosed in a number of patents, most notably U.S. Pat. No. 3,862,861. Such batteries normally utilize as separators materials such as microporous rubber, polyvinyl chloride, polyolefins, phenolic resin impregnated paper or (preferably) glass paper made from microfiber diameter, unwoven, short staple glass fibers. These batteries, while useful in a wide variety of applications, have been severely limited in the practical sizes which can be commercially utilized because of the high cost of these batteries per unit of energy density. Thus, while cells of the common C, D, "beer can" and similar sizes are practical for some purposes commercially, larger sizes such as the typical automotive battery size are far too costly for commercial practicality. Similarly, the high unit density cost of even the smaller size batteries have restricted these types of batteries to high value end uses such as in spacecraft and emergency equipment, effectively eliminating the batteries from the fields of conventional consumer use such as flashlights, radios and the like.
In these types of batteries a very high proportion of the cost of battery materials lies in the cost of the separator. The preferred microfiber glass paper separators are extremely costly. In the past, however, all attempts to substitute lower cost materials have led to battery structures with significantly poorer electrical characteristics.
It would therefore be highly desirable to have a separator material (as defined herein) suitable for use in batteries of the type described which will provide equivalent or superior electrical characteristics as compared to the present high cost materials, but which would utilize materials having a markedly lower cost than the present materials, thus making the batteries economically feasible for use in a much wider range of applications, particularly including the automotive ("SLI") battery market.